1. Field of the Invention:
The present invention relates to an electrochromic display device wherein an electrochromic layer present in solid form upon an electrode is in contact with an electrolyte, and to a method of producing the same.
2. Description of the Prior Art:
Display devices of the above-mentioned type are already known from the German published specifications Nos. 2,125,337; 2,201,104; 2,201,139 and 2,363,306. Such display devices contain as an essential constituent a cell of laminated structure to be controlled electrically which, in a particularly simple form of construction, exhibits on the side confronting the observer a glass plate upon which a transparent electrode made of tin dioxide is applied, which is adjoined by an electrochromic layer of tungsten or molybdenum trioxide, an electrolytic liquid layer, possibly a glycol-sulphuric acid mixture, and a further, preferably metallic, electrode. Under the influence of an electric field, the liquid electrolyte which is in direct contact with the electrochromic layer causes a rapid and uniform modification of the absorption characteristic in large areas of the electrochromic material and thus permits a rapid and uniform indication. A coloration occurs as a colored film on the electrode. The chromoactive ions of the electrochromic layer therefore do not pass into solution, but remain in the solid electrochromic layer. However, the short switching times which are necessary for a rapid indication are only achieved by applying a relatively high service voltage (U&gt;2V) to the cell electrodes, whereby the operational reliability and service life of the indicating devices are considerably reduced with a simultaneous undesirable increase in the energy consumption.